Chapter 5. Nicotinic Acetylcholine Receptors: Molecular Biology, Chemistry and Pharmacology

Enantioselective Construction of C3-Multifunctionalization α-Hydroxy-β-amino Pyridines via α-Pyridyl Diazoacetate, Water, and Imines for Drug Hunting

An asymmetric catalytic approach for the construction of C3-multifunctionalization α-hydroxy-β-amino pyridines has been reported. The products can be accessed by the modulation of two chiral catalysts independently in high yield and with good enantioselectivity. The method features mild reaction conditions and an excellent functional group tolerance. Biological activity analysis shows that the resulting products have a selective antiosteosarcoma activity on 143B cells.

Combinatorial synthesis of nicotine analogs using an Ugi 4-CR/cyclization-reduction strategy

A practical one-pot synthesis of nicotine analogs from Ugi 4-CR/propargyl adducts is reported. This methodology allows the rapid construction of the pyrrolidine moiety present in nicotine through an intramolecular base-promoted 5-endo cycloisomerization process, followed by a reduction of the resulting mixture of 2- and 3-pyrrolines to afford nicotine analogs in good overall yields.

Syntheses of (+)-Cytisine, (−)-Kuraramine, (−)-Isokuraramine, and (−)-Jussiaeiine A

Total syntheses of (+)-cytisine, (-)-kuraramine, (-)-isokuraramine, and (-)-jussiaeiine A were achieved via a samarium diiodide-promoted reductive deamination reaction, followed by simultaneous recyclization of a proline derivative to give the corresponding delta-lactam derivative, as a key step.

Total synthesis of (+/-)-cytisine via the intramolecular heck cyclization of activated N-alkyl glutarimides

[reaction:see text] A synthesis of racemic cytisine 1 has been developed utilizing an intramolecular Heck cyclization to prepare the bridged tricyclic intermediate 2. The cyclization employs activated glutarimide-derived ketene aminals 3 (X = P(O)OEt(2) or SO(2)CF(3)) and represents the first use of such intermediates in metal-catalyzed processes.

Recombinant human receptors and functional assays in the discovery of altinicline (SIB-1508Y), a novel acetylcholine-gated ion channel (nAChR) agonist

Neuronal nicotinic acetylcholine receptors (nAChRs) are a class of ion channels with significant potential as molecular targets for the design of drugs to treat a variety of CNS disorders. The discovery that neuronal nAChRs are further subdivided into multiple subtypes suggests that drugs which act selectively at specific nAChR subtypes might effectively treat Parkinson's disease (PD), Alzheimer's disease (AD), schizophrenia, ADHD, depression, anxiety or pain without the accompanying adverse side effects associated with non-selective agents such as nicotine (1) and epibatidine. Altinicline (SIB-1508Y) is a novel, small molecule designed to selectively activate neuronal nAChRs and is undergoing clinical evaluation for the treatment of PD. It was selected from a series of compounds primarily on the basis of results from functional assays, including (a) measurement of Ca2+ flux in stable cell lines expressing specific recombinant human neuronal nAChR subtypes; (b) determination of in vitro and in vivo neurotransmitter release; (c) in vivo models of PD. Biological data on both altinicline and the series of compounds from which it was selected are reported.

Central nicotinic receptor ligands and pharmacophores

Multiple populations of pentameric nicotinic acetylcholinergic (nACh) receptors exist and several may be classified as central or neuronal. Neuronal nACh receptors, however, are primarily of the alpha 4 beta 2 and alpha 7 types, and these have been the focus of most recent investigations aimed at the development of novel agents and identification of pharmacophores. Selectivity data are limited. Furthermore, because several populations of nACh receptors might indirectly influence a given functional effect, it is difficult to discuss structure-activity relationships (SAR) in terms of differential SAR, or to formulate SAR on the basis of functional studies. For the most part, studies are limited to the formulation of structure-affinity relationships (SAFIR) for the binding of agents at nACh receptors, and for these the alpha 4 beta 2 population has been the most extensively investigated. SAFIR and newer agents are reviewed here with reference to earlier studies. Novel agents now have been identified that bind with up to 30 times higher affinity than nicotine and these are providing new insight into the understanding of nACh receptors.

Synthesis and preliminary pharmacological evaluation of some cytisine derivatives

Thirty-one N-derivatives of cytisine were prepared in order to modify its pharmacological profile and to obtain compounds of potential therapeutic interest either at a peripheral or central level, particularly as nicotinic ligands with improved ability to cross the blood-brain barrier. Actually, with the introduction of different kinds of substituent on the basic nitrogen of cytisine a variety of activities were observed, both in vivo (analgesic, dopamine antagonism, antihypertensive, inhibition of stress-induced ulcers, antiinflammatory, protection from PAF-induced mortality, hypoglycemic) and in vitro (positive cardio-inotropic, beta-adrenergic antagonism, alpha 1- and alpha 2-antagonism, inhibition of PAF-induced platelet aggregation). Six randomly selected compounds were tested for the ability to recognize a central nicotinic receptor and four of them exhibited Ki values in the range 30-163 nM.

Conformationally restricted analogues of nicotine and anabasine

A series of conformationally restricted analogues of nicotine has been synthesized and evaluated as agonists of neuronal acetylcholine receptors. Compound 2 (SIB-1663), which selectively activated human recombinant alpha 2 beta 4 and alpha 4 beta 4 nAChRs, was shown to be active in animal models of Parkinson's disease and pain.

Nicotinic antagonists (piperidines and quinuclidines) reduce the susceptibility of early sea urchin embryos to agents evoking calcium shock

1. Some nicotinic antagonists (piperidine and quinuclidine derivatives and bis-quaternary compounds) protect early embryos of the sea urchin Lytechinus pictus against a calcium shock evoked by ionomycin or a mixture of phorbol myristate acetate and nicotine. 2. Maximal protective potency was found for drugs that did not penetrate the plasma membrane. 3. Early sea urchin embryos have nicotinic acetylcholine receptors (nAChR) or nAChR-like structures localized on the cell surface that, apparently, take part in the control of Ca2+ influx.

Inherited, selective hyporesponsiveness to the analgesic action of nicotine in mice

The acute dose-dependent analgesic activity of nicotine, as measured by the tail-flick assay, differed significantly between CD-1 and CF-1 outbred strains of mice. Differing responsiveness to the tail-flick stimulus did not explain this pharmacological effect. The inherent analgesic hyporesponsiveness of CF-1 mice was pharmacologically selective. Xilocaine and morphine produced an analgesic response of large magnitude in CF-1 mice. Reduced efficacy of nicotine in the CF-1 analgesia assay was not observed in its action on locomotor activity or in the induction of seizures and lethality. These findings have practical significance in identifying the importance of genotype in choice of strain for preclinical pharmacological studies of nicotine-induced analgesia and indicate that genetic analysis may provide a valuable tool for investigating the mechanism underlying the analgesic action of nicotine.